My experience with .44-40 has been in a Colt SAA (1914 production) and Marlin 1894 (1905 production). Observations (in no particular order):

1. .44-40 is a bottle-necked cartridge. No carbide sizer dies, case lube required.

2. Case walls and case mouths are quite thin (compared to most of the more modern designs). Easy to damage a case mouth or collapse a case wall while seating bullets, careful attention to case mouth expansion is required to avoid scrapping a lot of brass. I recommend the Lyman M-die, two-step expander to ease starting the bullet. Also note: bullet diameter will dictate case mouth expansion (see further comments on variations in bore/groove dimensions).

3. Very wide variations in chambers and bores are known to exist. The chamber throats of my Colt are 0.426" diameter, dictating the older small diameter bullets. The Marlin has 0.430" groove diameter, so the larger bullet diameters shoot better. I developed one load that I can use in both, consisting of a relatively soft cast bullet 0.427" as cast, lubed but not sized. Works fine in the Colt, "bumps up" enough on firing to shoot accurately in the Marlin. For those with larger diameter throats, bores, grooves and using .429" or .430" bullets I would recommend ordering the appropriate expander stem for the Lyman M-die to accept those bullets without undue stress on the cases during seating.

4. Marlin has a tubular magazine so a good crimp is necessary to prevent bullet set-back. I use a firm roll crimp in the crimp groove of the cast bullets and have had no problems with set-back. Flat-nose bullets, of course, for the tubular magazines.

5. With the thin case walls and case mouths, and the repeated stresses involved in neck expansion and crimping I do not expect long lives with my .44-40 brass. Metal fatigue is likely to be greater than we see in .44 Special or Magnum brass.

6. I have been advised by an experienced .44-40 user that brass can be made from .45 Colt, case head and body diameters being close enough to allow reforming to .44-40. I have not had to try this yet, but with current shortages it might be an alternative. If I were trying this I would start with a few dummy rounds with bullets seated and crimped, checking to verify they will chamber properly (easily), and only then would I continue to a few actual loaded rounds to test before I loaded up a quantity of ammo with such resized cases.

Hope this helps.